This invention relates to a method and apparatus for pumping viscous and abrasive fluids, including slurries (hereinafter process fluid). The apparatus may particularly be a hydraulic operated displacement pump adapted to be built into pipe line systems. The method of the present invention comprises using a working fluid to pump the process fluid by means of pumping an intermediate fluid compatible with the process fluid continuously through a conduit system and using the intermediate fluid to force the process fluid through a pumping zone. The apparatus of the present invention preferably comprises a pumping element consisting of at least one tubular diaphragm pump provided with check valves and a power section. The pumping element is an integral part of the pipe line system in which the actual process fluid is to be transported. The power section is a separate unit connected to the pumping element by a conduit system for the intermediate working fluid.
Known pumps of this type are piston-diaphragm pumps and hose-diaphragm-piston pumps. In the first mentioned type of pump, the diaphragm is situated between the working fluid and the process fluid. In the latter type of pump, a tubular flexible separating wall is situated between the working fluid and process fluid and the diaphragm is situated between the first-mentioned working fluid and a second working fluid. Tubular diaphram pumps of this type are characterized by the ability to pump abrasive material, material having a thick consistency, various types of sludge, chemically active fluids, etc. Furthermore, such pumps can be used at very high pump pressures as a result of the hydraulic equilibrium between the working and process fluids. This permits the pumping of higher-density fluids than with centrifugal pumps, which means that a smaller volume of material needs to be pumped (in the case of a slurry) to transport a given amount of solid. This results in lower costs and consumption of less energy per unit of solids. Another advantage of diaphragm pumps over conventional pump types is the lack of movable connections into the process fluid, as a result of which the danger of contamination of the process fluid is greatly diminished. However, due to the fact that the pistons for pressurizing the first and/or second working fluid are mechanically operated, diaphragm pumps are relatively bulky and, as a result, problems often arise in mounting them. Although a tubular diaphragm pump of the foregoing type is usually preferable, it has often been necessary to choose another pump type which is less bulky, although the other pump type is otherwise not as advantageous as a tubular diaphragm pump.